Early Rearing of Cutthroat Trout Technical Report

Home , Lahontan cutthroat trout

western regional aquaculture center

Compiled by Gary Fornshell, University of Idaho Extension Christopher Myrick, Colorado State University

United States Department of Agriculture National Institute of Food and Agriculture 1 2 Project Participants

Christopher Myrick, Colorado State University

Mandi Brandt, Colorado State University

Rick Barrows, US Department of Agriculture

Ken Cline, Cline Trout Farms

Gary Fornshell, University of Idaho Extension

Greg Kindschi, US Fish and Wildlife Service

Molly Webb, US Fish and Wildlife Service

Kevin Kappenman, US Fish and Wildlife Service

Jeremy Liley, Liley Fisheries, Inc.

Photo credits: Cover: Dec Hogan/iStock/Thinkstock Above: U.S. Geological Survey/photo by Jonny Armstrong 3i Table of Contents

Background 1 native Cutthroat 2 Early Rearing Research 5 optimizing Feed 5 research Findings and Recommendations 5 supplementing Live Artemia 6 Water Temperature 7 rearing Density 8 temperature Test Results 8 rearing Density Test Results 10 Production Scale Trial 10 cost-Benefit Matrix 11 Summary 11 suggested Readings 12 Acknowledgments inside back cover

4ii Figures

1. Map showing the distribution of extant cutthroat trout subspecies in the western United States 4 2. comparison of the effects of diet on the coloration of juvenile Colorado river cutthroat trout 7 3. a small-scale Artemia hatching system 8 4A. Effects of water temperature on the final wet weights of juvenile Snake river cutthroat trout 9 4B. effects of water temperature on the final wet weights of juvenile Yelllowstone cutthroat trout 9 5A. Final wet weights of Colorado River cutthroat trout fed the regular Trout co. #1 + Artermia 9 5B. Final wet weights of Colorado River cutthroat trout fed the Premium Trout Co. #3 + Artemia 9

Tables

1. Primary state agency responsible for regulating aquaculture in the western United States 1 2. Protein and fat percentages of the feeds used in the cuttthroat trout early rearing study 5 3. Feeds used in the supplemental feeding trial with juvenile Snake River cutthroat trout 5 4. Final wet weights for Snake River, Yellowstone, and Colorado River cutthroat trout fed on a variety of commercially available or open-formula diets 6 5. effects of rearing density on the growth of first-feeding Colorado river cutthroat trout 10 6. cost-benefit matrix for Colorado River cutthroat fed one of three diet combinations 12 7. cost-benefit matrix for Snake River cutthroat fed one of two diets 12

iii5 6 Background

The charm of fishing is that it is the pursuit of what is elusive but attainable, a perpetual series “ of occasions for hope. —John Buchan ” Cutthroat trout (Oncorhynchus clarkii) are popular game species are allowed for propagation. Table 1 below lists the fish in the western United States. For private fish farmers, state agency responsible for regulating aquaculture in each they represent a potential high-value fish for profitable rec- of the western states. State aquaculture coordinators can reation-based aquaculture. Cutthroat trout are potentially provide information about aquaculture regulations. For more valuable for the recreational market than the more a directory of state coordinators, go to the National common rainbow trout (Oncorhynchus mykiss) because Association of State Aquaculture Coordinators website they are in limited supply and are considered by some to (http://www.nasac.net/). Alternately, you can contact your be more aesthetically pleasing. County Extension Office for assistance. Propagation of cutthroat trout in public hatcheries is The Western Regional Aquaculture Center (WRAC) also necessary for conservation and restoration programs. recently completed a study on the economic contributions They are primarily produced for put-and-grow fisheries, thus placing a premium on high rates of fry and juvenile Table 1. Primary state agency responsible for regulating survival, and good fry quality (i.e., intact fins and oper- aquaculture* in the western United States. cula). However, insufficient knowledge of the optimal early rearing culture requirements has led fish culturists to use State Department conditions similar to those for rainbow trout with variable success. Arizona Department of Agriculture Lack of specific feeds for cutthroat trout is one factor California Department of Fish and Game that contributes to inconsistent and non-repeatable Colorado Department of Agriculture growth, survival, and quality from year to year. Two other critical factors that substantially influence fish perfor- Idaho Department of Agriculture mance are rearing temperature and rearing densities. Montana Department of Fish, Wildlife, and Parks Optimizing early rearing by focusing on feed, water tem- Nevada Department of Wildlife perature, and rearing density should result in improved New Mexico Department of Game and Fish growth, quality, and survival. Ultimately, fish culturists Oregon Department of Fish and Wildlife that optimize early rearing conditions for cutthroat trout will produce a fish desired by both customers of the Utah Department of Agriculture private recreation-based aquaculture sector and the public Washington Department of Fish and Wildlife hatcheries engaged in conservation and restoration efforts. Wyoming Department of Game and Fish Aquaculture producers of recreational fish are located * some states have two departments co-regulate aquaculture throughout the western states with the majority in Cali- where one department may issue a fish propagation license fornia, Colorado, Oregon, and Washington. State regula- and another department regulates species allowed and impor- tions for private aquaculture production vary, including tation requirements. which state departments regulate aquaculture and which

1 of the private, recreation-based aquaculture industry in • Cutthroat trout are generally spring spawners, a trait the western United States (depts.washington.edu/wracuw/ that can increase the likelihood of hybridization (inter- research/starter-diets_trout.html). Western suppliers of breeding) with the closely related rainbow trout. recreational fish generate annual sales of $57.2 million and • Their natural diet consists primarily of insects (both 1237 jobs. The total annual economic contribution of this aquatic and terrestrial) and other aquatic invertebrates, important aquaculture sector in the West is $108.2 mil- though larger fish will also start to feed on other fish. lion. A variety of cold-, cool-, and warm-water species are • Because they are very closely related to rainbow trout, sold to recreational outlets, to brokers, as food fish, and to cutthroat trout readily interbreed to produce cuttbows, other markets. The majority of salmonids (88%) are sold a hybrid cross that can sometimes breed on its own. to public and private recreational outlets, such as private This propensity to hybridize with rainbow trout is fisheries, fishing clubs, municipalities, and home owner one of the reasons cutthroat trout subspecies declined associations. Only a small percentage of salmonids are throughout their range—as rainbow trout were intro- sold to brokerages. Almost all salmonids produced in the duced, the pure lines of cutthroat trout hybridized and western region are sold within the western states. declined in fitness, range, and abundance. • Like all trout and salmon, they build redds, typically Native Cutthroat TROUT in the gravel of streams, rivers, or the inlets and outlets The western United States was home to a variety of of ponds and lakes. Egg incubation times vary with cutthroat trout (O. clarkii), including at least 11 distinct water temperature. subspecies or strains of which approximately 9 were still • All cutthroat trout are excellent sportfish, responding extant in 1992 (Figure 1). Historical distribution of cut- favorably to flies, lures, and bait. They are often prized throat trout subspecies included temperate rainforests by anglers for their coloration and vigorous fighting of the Pacific Northwest, pluvial basins within the Great abilities. Basin, subalpine areas of the Rocky Mountains, and high deserts of the Southwest. These fish, while closely related The focus of this paper is on the optimization of early to rainbow trout (O. mykiss), were found primarily in rearing techniques for three subspecies of cutthroat trout: inland drainages, while the strongholds of rainbow trout the Colorado River cutthroat trout (O. c. pleuriticus), the were the coastal drainages. The inland cutthroat trout Yellowstone cutthroat trout (O. c. bouvieri), and the Snake were able to take advantage of a diverse range of habitats River cutthroat trout (O. c.). These subspecies were chosen and occurred in everything from tiny headwater streams for a variety of reasons, including their availability in to large rivers and very large lakes (e.g., Lake Tahoe on large enough numbers to permit controlled laboratory the California–Nevada border). studies, their relationships to other cutthroat trout (e.g., Not surprisingly, this diverse group of habitats also the Colorado River cutthroat trout is closely related to led to a diverse set of life history strategies, with some the greenback cutthroat, O. c. stomias, and Rio Grande fish acting much like anadromous salmon, living in large cutthroat trout, O. c. virginalis), and the growing demand lakes and migrating into rivers to spawn, while others were from fish culturists for information on these species. resident in rivers and streams year-round. In terms of size, The Colorado River cutthroat trout was originally found mature cutthroat trout also varied widely—one extinct throughout the upper Colorado River drainage, with lineage of Lahontan cutthroat trout that used to inhabit populations in Colorado, Wyoming, Utah, Arizona, and Lake Tahoe grew to more than 40 pounds, while some New Mexico. Like most other native cutthroat in the varieties that lived in small headwater streams rarely western United States, they have experienced a drastic exceeded two pounds. decline in their range and are now typically found only Despite the wide variety of habitats and life history in isolated headwater portions of streams and lakes. strategies exhibited by cutthroat trout, the various sub- Because of their once wide distribution, they are one of species do share some key characteristics that should be the more popular candidate subspecies for use in stocking of interest to fish culturists. native fish.

2 Colorado River cutthroat trout Kevin Rogers Kevin

Yellowstone River cutthroat trout Kevin Rogers Kevin

Snake River cutthroat trout Kevin Rogers Kevin

Originally native to the Yellowstone River drainage, Closely related to the Yellowstone subspecies, the the Yellowstone cutthroat subspecies was historically Snake River cutthroat subspecies originally occurred in found in Montana, Wyoming, Idaho, and Nevada. They the Snake River drainage. Its distribution is not shown on have experienced drastic declines in range and population Figure 1 because it is likely the most widely introduced size; one population in particular, the fish in Yellowstone subspecies and has been spread throughout the western Lake, is under continued threat from competition and states, either as a pure cutthroat trout, or, more commonly, predation with non-native salmonids. The Yellowstone as a cuttbow. It is a very popular sportfish; because of its Lake population used to thrive in such numbers that the rather distinct coloration, it can be favored by fisheries spawning run into lake tributaries was compared to that of management agencies for stocking because it can be Pacific salmon in Alaska and supported a large variety of easily distinguished from the native cutthroat trout terrestrial predators, including grizzly bears and bald eagles. subspecies.

3 WA

MT 10 1 OR ID 11 7 8 WY 6

5 9 4 NV UT 3 CA CO

1 Coastal 7 Alvord 2 Rio Grande 8 Whitehorse 3 Greenback 9 Bonneville 4 Colorado River 10 Westslope

5 Lahontan 11 Yellowstone

6 Humboldt

Figure 1. Map showing the distribution of extant cutthroat trout subspecies in the western United States. Data are from Behnke 1992. The Snake River cutthroat has been widely introduced and is not shown on this map.

4 Early rearing research

Unlike rainbow trout, which have a long and rich history Table 2. Protein and fat percentages of the feeds used in the of research on culture techniques and requirements, cutthroat trout early rearing study. inland cutthroat trout remain relatively unknown from a culture standpoint. There has been some research on feed protein (%) fat (%) culture techniques, but this has been conducted mainly on a state-by-state basis when small numbers of fish were Regular Trout Co. #1 50.8 16.0 being produced for species conservation or restoration Soft Moist Co. #1 38.4 18.9 purposes. Even in those situations, fish culturists often Regular Trout Co. #2 50.5 17.5 relied on rainbow trout culture techniques and diets, and found that the level of success was not as high as it was Soft Moist Co. #2 48.9 15.0 with rainbow trout. Premium Trout Co. #3 53.7 18.4 Therefore, the purpose of this WRAC research project USDA Experimental was to develop culture techniques specifically for juvenile #601 (E601) 51.1 18.8 Colorado River, Snake River, and Yellowstone cutthroat trout. The research team focused on three areas: optimiz- USDA Experimental ing feed, water temperature, and fish rearing density. #602 (E602) 42.4 17.6

Optimizing feed Premium Trout Co. #3 + live Artemia (Colorado River cutthroat trout only) Rather than go through the process of developing a cutthroat-specific diet, the team chose to test a set of commercial feeds from three feed manufacturers and two open formula feeds to identify existing diet formula- tions that would result in high growth rates and survival. Table 3. Feeds used in the supplemental feeding trial with Additionally, one subset of the research team also inves- juvenile Snake River cutthroat trout. The goal of this tigated the effect of using live Artemia (brine shrimp) as feeding trial was to determine if other premium feeds with a supplement during first feeding of juvenile Colorado or without supplements such as cyclopeeze would also River cutthroat trout on fish growth and survival. The provide rapid growth and high survival. feeds used in the study are shown in the Table 2. Following the encouraging results of the initial diet trial (120 days with a water temperature of 50.5°F feed [10.3°C]), a supplemental feed trial was conducted on Premium Trout Co. #3 Snake River cutthroat trout to determine whether other premium feeds or supplements would provide the same Premium Trout Co. #3 + dry Artemia flake benefit as was seen with the Premium Trout Co. #3 + live Premium Trout Co. #3 + freeze dried cyclopeeze Artemia. The feeds used in this additional trial are shown Salmon Fry Micro Pellet Co. #2 in Table 3. Premium Larval Co. #4 Research Findings & Recommendations Premium Larval Co. #4 + freeze dried cyclopeeze Fish were fed 4% of body weight per day using automatic Regular Trout Co. #2 belt feeders. The best feed in terms of both survival and growth for Snake River cutthroat trout was the Premium Trout Co. #3, with fish gaining an average of 4.78 g/fish

5 (~ 95 fish/pound) over the 120-day trial, and survival Supplementing Live Artemia exceeding 97%. The best diet for Yellowstone cutthroat trout was also the Premium Trout Co. #3, with fish fed that diet gaining 3.73 g/fish (~ 122 fish/pound) and survival of Artemia were cultured based on recommenda- > 97%. For the Colorado River cutthroat trout, the best tions by Granvil D. Treece, Artemia production non-supplemented diets in terms of growth were: for marine larval fish culture. Southern Regional 1) Regular Trout Co. #1 (4.20 g/fish, ~107 fish/pound; Aquaculture Center, Publication 702, Stoneville, survival of 78.5%), 2) USDA Experimental #601 (3.90 g/ Mississippi (https://srac.tamu.edu/index.cfm/ fish, ~116 fish/pound; survival of 68.0%), and 3) Premium event/getFactSheet/whichfactsheet/142/) Trout Co. #3 (3.89 g/fish, ~ 117 fish/pound, and survival of 77.5%). However, when the Premium Trout Co. #3 + Cutthroat trout were fed 4% body weight based Artemia feed is included, the Artemia supplementation led on the weight of the Artemia cysts, adjusted for to a 31% increase in final fish size to 5.12 g/fish (~ 89 fish/ an estimated 90% hatch rate, for the first 14 days pound) and a 5.7% increase in survival. Dorsal fin index, of feeding. From days 15 to 21 fish were fed the a measure of fin condition used as a metric of fish perfor- premium starter feed and Artemia, with each mance, was unaffected by diet for all three cutthroat trout feed fed at 2% of body weight. After 21 days of subspecies tested. feeding, the fish were fed exclusively the pre- In Table 4 below, final wet weights in grams/fish and pared trout feeds. Artemia were fed within (fish/pound) after 120 days at 50°F (10°C) water tempera- 4 hours of hatching to minimize nutritional ture for the three subspecies of cutthroat trout are shown. loss. Artemia were introduced at the inlet of Final weights are based on average weights of all fish per each tank with a syringe. treatment. One interesting side-note from the Colorado River cutthroat trout studies was that the different diets produced significant differences in fish color (see Figure 2).

Table 4. Final wet weights (grams per fish, fish/pound in parentheses) for Snake River, Yellowstone, and Colorado River cutthroat trout fed a variety of different commercially available or open-formula diets.

Snake River Yellowstone colorado River feed Cutthroat Trout Cutthroat Trout Cutthroat Trout

1. Regular Trout Co. #1 3.56 (127) 2.74 (166) 4.20 (108) 2. Soft Moist Co. #1 2.77 (164) 2.17 (209) 1.83 (248) 3. Regular Trout Co. #2 4.03 (113) 3.17 (143) 3.80 (119) 4. Soft Moist Co. #2 3.76 (121) 2.94 (154) 2.24 (203) 5. Premium Trout Co. #3 4.78 (95) 3.73 (122) 3.89 (117) 6. USDA Experimental #601 (E601) 3.78 (120) 2.74 (166) 3.90 (116) 7. USDA Experimental #602 (E602) 3.82 (119) 2.84 (160) 3.10 (146) 8. Premium Trout Co. #3 + live Artemia not tested Not tested 5.12 (89) (Colorado River cutthroat trout only)

Diet #7 Diet #4

Diet #1 Diet #5

Diet #3 Diet #8

Diet #2 Diet #6 Mandi Brandt

Figure 2. Comparison of the effects of diet on the coloration of juvenile Colorado River cutthroat trout.

When subjected to a quantitative ranking by a team of Additionally, the difference in weight between the fish fed trained observers, E601 produced fish with the deepest Premium Trout Co. #3 and those fed Premium Trout Co. reds, followed by Premium Trout Co. #3, Premium Trout #3 + Artemia, Premium Trout Co. #3 + dry Artemia flake, Co. #3 plus Artemia, Regular Trout Co. #1 and Soft Moist Premium Trout Co. #3 + freeze-dried cyclopeeze, Premi- Co. #2, Regular Trout Co. #2, and, at the yellow end of the um Larval Co. #4, Premium Larval Co. #4 + freeze-dried spectrum, Soft Moist Co. #1 and E602. cyclopeeze were not significant, indicating that for Snake An additional 65-day diet trial was performed at the River cutthroat trout at least, there is no clear benefit to Bozeman Fish Technology Center in Montana, to compare diet supplementation, and, more importantly, that the use the effects of different diet supplements on the growth, of any typical premium diet provides a similar level of survival, and performance of Snake River cutthroat trout. growth performance. The supplements used were: Artemia Premium Trout Co. Based on these results, it is clear that the Premium #3, Premium Trout Co. #3 + dry Artemia flake, Premium Trout Co. #3 diet, or a similar high-performance diet, is Trout Co. #3 + freeze-dried cyclopeeze, Salmon Fry Micro ideal for first-feeding of juvenile cutthroat trout, irrespec- Pellet Co. #2, Premium Larval Co. #4, Premium Larval Co. tive of subspecies. Additionally, supplementation of the #4 + freeze-dried cyclopeeze, and Regular Trout Co. #2. prepared diets with live Artemia during the first 21 days The results of this additional diet trial demonstrated of feeding can confer a significant growth and survival that other starter diets (both premium and non-premium) advantage, particularly in cases where overall survival produced the same high levels of survival (> 93%) with is lower than that seen at the Bozeman Fish Technology Snake River cutthroat trout as did Premium Trout Co. #3. Center. Finally, if fish color is important, Premium Trout

7 Co. #3, Premium Trout Co. #3 + Artemia, or any diet with Typically, as the density of the fish increases past some astaxanthin supplementation (e.g., E601) can dramatically threshold level, there is an increase in the amount of fin change the appearance of the fish. erosion seen, and a decrease in growth rates. The research team wanted to test the effect of rearing density (using the Water temperature best diet and best temperature identified in the research trials) on growth, survival, and fish appearance (fin Cutthroat trout are generally regarded as having a lower condition). optimal growth temperature than rainbow trout. For example, Westslope cutthroat trout (O. clarkii lewisi) have an optimal growth temperature of 56.5°F (13.6°C), but the Temperature TEST RESULTS actual optimal growth temperatures had not been estab- All subspecies of cutthroat trout tested showed a classic lished for the three subspecies in question. We compared temperature × growth response, with lower growth rates at the growth and survival of the fish when reared at tem- the lower temperatures, increasing growth as the tempera- peratures between 50 and 68°F (10 to 20°C) to develop ture approached the growth optimum, and then a decline temperature × growth curves and identify the optimal in growth at temperatures above that optimum. For the growth temperature for cutthroat trout fed the best diets Snake River cutthroat trout the optimal growth tempera- identified previously. ture was 58°F (14.5°C) (Figure 4a), and for the Yellowstone cutthroat trout, the optimal growth temperature was Rearing density 58.5°F (14.7°C) (Figure 4b). Survival of both Snake River cutthroat trout and In salmonid culture, fish culturists try to achieve a com- Yellowstone cutthroat trout was uniformly high in the promise between raising a high density of fish per unit study, and independent of temperature. volume of water (maximizing the efficiency of their water The results for the Colorado River cutthroat trout usage) and the appearance and performance of the fish. follow the same pattern, with an optimal growth temperature for fish fed Regular Trout Co. #1 + Artemia of 59.5°F (15.3°C), and an optimal growth temperature for fish fed Premium Trout Co. #3 + Artemia of 61.5°F (16.4°C; Colorado River cutthroat trout survival was inversely correlated with temperature, with higher survival at the lower temperatures tested. This particular result is interesting as it suggests that different diet compositions and perhaps digestibilities can affect the optimal growth temperature. Most importantly, however, it highlights the importance of conducting pilot-scale comparisons of various premium diets in individual facilities to identify the diet that gives the best performance under facility- specific conditions. (Figures 5a and 5b). In a similar study, Bear et al. (2007) reported that the optimal temperature for growth of another cutthroat trout subspecies, the Westslope cutthroat, was 13.6°C when reared in the same multi-temperature apparatus as the Figure 3. A small-scale Artemia hatching system. Snake River and Yellowstone cutthroat trout. These fish Aquarium heaters maintain the optimal water temperature were not first-feeding cutthroat, ranging from 9.4–19.3 g for hatching, while the lights allow concentration of the at the start of the study, but it does show that these fish are hatched nauplii for harvest. Running dual hatching similar to the other cutthroat trout subspecies, and that chambers provides insurance in case of a failed hatch they seem to thrive in slightly cooler water than is typically in a single chamber. used for rainbow trout culture.

8 The results of the temperature trials suggest that it range. Prospective growers should also recognize the should be possible to rear juvenile cutthroat trout of importance of using a premium diet, and, as mentioned various subspecies in facilities that have been optimized above, test various premium diets to see which ones for rearing rainbow trout because the optimal growth give the best performance under their specific culture temperatures are within the same 57–61°F (14–16°C) conditions.

4.5 9 4 8 3.5 7 6 3 5

Wet Weight (g) Weight Wet 2.5 4

2 3 2 8 10 12 14 16 18 20 22 (day 120) Weight Mean Wet 10 11 12 13 14 15 16 17 18 19 20 21 22 Temperature (°C) Temperature (°C)

Figure 4a. Effects of water temperature on the final wet Figure 5a. Final wet weights (tank means) of Colorado weights of juvenile Snake River cutthroat trout at the River cutthroat trout fed the Regular Trout Co. #1 + conclusion of the 120-day growth study. Data points rep- Artemia. The optimal temperature for growth was deter- resent tank means. The shaded area is the 95% confidence mined to be 15.3°C. The data points are tank means, and interval for the curve fit. Optimal temperatures for growth the shaded area shows the 95% confidence interval for the are mentioned in the text. fitted regression expression.

6 12 5.5 11 5 10 4.5 9 4 3.5 8 Wet Weight (g) Weight Wet 3 7 2.5

Mean Wet Weight (day 120) Weight Mean Wet 6 8 10 12 14 16 18 20 22 10 11 12 13 14 15 16 17 18 19 20 21 22 Temperature (°C) Temperature (°C)

Figure 4b. Effects of water temperature on the final wet Final wet weights (tank means, g) of Colorado River cut- weights of juvenile Yellowstone cutthroat trout at the throat trout fed the Premium Trout Co. #3 + Artemia. The conclusion of the 120-day growth study. Data points rep- optimal temperature for growth was determined to be resent tank means. The shaded area is the 95% confidence 16.4°C. The data points are tank means, and the shaded interval for the curve fit. Optimal temperatures for growth area shows the 95% confidence interval for the fitted re- are mentioned in the text. gression expression.

9 Rearing Density TEST RESULTS as one would grade rainbow trout. Again, the use of a The Snake River cutthroat trout and Yellowstone cut- premium diet may help to reduce the onset of density- throat trout were tested at densities of 50 to 350 fish per dependent growth effects and may also have played a role 26.42 gallon tank (100-L tanks) at 58°F (14.5°C) and fed in preventing fin erosion problems, though this was not Premium Trout Co. #3, while the Colorado River cutthroat directly tested in this set of experiments. trout were tested at densities of 150, 300, 450, and 600 fish per 26.42 gallon tank (100-L tanks) at 61.5°F (16.4°C) and Production-scale Trial fed the same diet. The final wet weights (and therefore, the A production-scale trial of Snake River cutthroat trout growth rates) of the Snake River cutthroat trout and was conducted at a commercial facility in Colorado. The Yellowstone cutthroat trout were slightly affected by fish in this trial were reared at an initial density of 350 fish rearing density; fish reared at 50 fish/tank weighed 20% per tank in 55.4–57°F (13–14°C) well water and were fed and 15% more, respectively, than Snake River cutthroat Premium Trout Co. #3 at the same rate as fish in the labo- trout or Yellowstone cutthroat in the 350 fish/tank groups. ratory studies (4% body weight/day). Other than the use Survival was unaffected by density, and fish condition of the recommended density and diet from the laboratory was uniformly high. When reared at 600 fish per tank, the studies, fish in the production trial were handled using Colorado River cutthroat trout had lower final wet weights regular rainbow trout production techniques. At the end compared to fish reared in the 150, 300, or 450 fish per of the 120-day trial, the fish were slightly smaller, at about tank groups, showing that at these higher densities one 125 fish/pound (3.62 g per fish), than the predicted weight can expect a reduction in fish size, even when ad libitum of 113–110 fish/pound (4.0–4.13 g per fish) expected under rations of a premium feed are provided. As with the other laboratory conditions, but the small 0.4–0.5 g difference two cutthroat trout subspecies, no difference in fin condi- suggests that the results of the laboratory studies accu- tion was observed, even at the highest density (see Table 5). rately predict performance under production conditions. The density results suggest that there is a critical point, Interestingly, post-experiment monitoring of the fish in the likely between 0.65 and 0.79 pounds fish per cubic foot production setting has identified a potential challenge to per inch (lb/ft3/inch) of fish length, where the increased commercial production of larger 8–12 inch (20–30.5 cm) density of fish starts to have a slight negative effect on fish cutthroat trout: the fish apparently experience a period of size. Given this information, it is recommended that initial slow growth from 4–8 inch (10–20 cm) relative to rainbow stocking densities be kept at or below 0.65 lb/ft3/inch of trout. Further WRAC-funded studies on eliminating this fish, and that as the fish increase in size, they be graded growth bottleneck are now underway.

Table 5. Effects of rearing density on the growth of first-feeding Colorado River cutthroat trout.

fISH DENSITY/TANK initial density FINAL DENSITY FINAL FISH Fish/pound 26.42 gal (1 gpm flow) (Lb/ft3)/inch (Lb/ft3)/inch WEIGHT (g) (approximately)

150 0.02 0.27 11.9 38 300 0.04 0.57 12.1 37 450 0.06 0.79 10.4 44 600 0.07 0.85 8.1 56 * Density index = weight of fish ÷ (fish length x volume of rearing unit)

10 Cost-Benefit Matrix plus Artemia with only a 50% hatch rate generated more Because there is a large price difference between regular revenue than the cutthroat trout fed the regular and trout feed and premium trout feed, we wanted to see if the premium-only feeds. Although the total cost per pound premium feed was cost-effective. Additionally, the cost of of feed fed is much higher for the premium trout plus feeding Artemia was calculated. The basis for the cost- Artemia, the growth performance of the cutthroat trout benefit matrix is the study done at Colorado State Univer- fed this diet more than compensated for the price differ- sity with Colorado River cutthroat trout. The thermal-unit ences (see Table 6, next page). growth coefficient (TGC) was calculated for the cutthroat A similar cost-benefit matrix for Snake River cutthroat trout fed the regular trout feed, the premium trout feed, trout is shown in Table 7 (next page). The basis for this and the premium trout feed plus live Artemia. The scenario is the performance of the best two diets con- thermal-unit growth coefficient is based on the exponent ducted at the Bozeman Fish Technology Center. One is a 1/3 power of body weight and accounts for water tempera- regular trout feed and the other is the premium trout feed. ture. TGC values and growth rate are dependent on Artemia was not fed, but all other assumptions used for species, strain, nutrition, husbandry, and other factors, the Colorado River cutthroat trout apply. The Snake River so it is necessary to determine the specific TGC value cutthroat trout fed the premium trout feed outperformed for a given production system based on growth records. those fed the regular trout feed and as a result, generated more pounds of fish and revenue.

1 1 ⎡ 3 − 3 ⎤ (Wf Wi ) TGC = = ⎢ ⎥×100 Summary ⎢ t ×°C ⎥ ⎣ ∑( ) ⎦ Research conducted at the Bozeman Fish Technology Wf = final live weight, expressed as grams Center and Colorado State University with three sub- Wi = initial live weight, expressed as grams species of cutthroat trout has shown that feeding a premium trout starter feed can confer greater growth than t = time, expressed as days a regular trout starter feed. Additionally, supplementation °C = water temperature degrees Celsius with live Artemia during the first 21 days of feeding can For the cost-benefit matrix, a more realistic hatchery water confer a significant growth and survival advantage. temperature of 57°F was selected rather than the optimum It is recommended that pilot-scale comparisons of of 61.5°F. Feed conversion ratios (FCR) were based on a various premium trout starter feeds be conducted to feed chart. A FCR of 0.75:1 was used for 1240 fish/pound identify which feed provides the best performance and smaller; 0.80:1 for fish greater than 1240/pound and under facility-specific conditions. The results of the water up to 1095 fish/pound; 0.85:1 for fish greater than 1095/ temperature trials suggest that it should be possible to pound and up to 287 fish/pound; 0.90:1 for fish greater rear juvenile cutthroat trout in facilities that have been than 287/pound and up to 114 fish/pound; 1.0:1 for fish optimized for rearing rainbow trout because the optimal greater than 114/pound and up to 56 fish/pound; and growth temperatures are within the same 57–61°F range. 1.05:1 for fish greater than 56/pound and up to 20 fish/ The density results suggest there is a critical point, likely pound. Feed sizes in the matrix ranged from #0 to 3/32 between 0.65 and 0.79 pounds of fish per cubic foot per (2.4 mm). Premium trout feed prices are for sizes #0, 1, inch of fish length, where the increased density begins to and 2. Cost calculations for the Artemia were done based negatively affect fish growth. The water exchange rate per on hatch rates of 90, 75, and 50%. The matrix assumed tank in the Colorado River cutthroat density study was 100,000 fish were grown. Feed and Artemia prices are about 3.5 per hour. It is recommended that initial stocking based on mid-year 2011 prices. An ex-farm price of $4.00 densities be kept at or below 0.65 pounds of fish per cubic per pound was assumed. foot per inch of fish length, and that as the fish grow, they Surprisingly the cutthroat trout fed the premium diet be graded as one would grade rainbow trout.

11 Table 6. Cost benefit matrix for the Colorado River cutthroat trout fed one of three diet combinations.

regular Premium premium trout feed trout trout + Artemia*

Feed Cost/lb fed ($) 0.69 0.75 0.95 1.01 1.17 Total Gain (lb) 3616 3702 5045 5045 5045 Difference in Total Gain (lb) 0 86 1429 1429 1429 Fish/pound 27.5 26.9 19.8 19.8 19.8 Difference in Total Revenue ($) 0 47 3341 3064 2232

* Based on 90, 75 and 50% hatch rate, respectively.

Table 7. Cost-benefit matrix for Snake River Cutthroat fed one of two diets.

regular premium feed trout trout

Feed Cost/lb fed ($) 0.67 0.73 Total Gain (lb) 3595 4251 Difference in Total Gain (lb) 0 656 Fish/pound 27.7 23.4 Difference in Total Revenue ($) 0 1840

SUGGESTED READINGS Brandt MM. 2009. Optimal starter diets and culture Kindschi GA, Myrick CA, Barrows FT, Toner M, Fraser conditions for Colorado River cutthroat trout WC, Ilgen J, and Beck L. 2009. Performance of (Oncorhynchus clarkii pleuriticus). M.S. Thesis. Yellowstone and Snake River cutthroat trout fry fed Deisenroth D and Bond C. 2010. The economic contri- seven different diets. North American Journal of bution of the private, recreation-based aquaculture Aquaculture 71(4):325–329. industry in the Western United States. Colorado State Piper RG and coauthors. 1982. Fish hatchery management, University, Fort Collins, CO. 1st edition. U. S. Fish and Wildlife Service, Washing- ton, DC, USA.

12 ACKNOWLEDGMENTS

This research was supported by Western Regional Aqua- National Fish Hatchery for supplying disease-free culture Center grant numbers 2005-35206-14718, 2006- Yellowstone and Snake River cutthroat trout eyed-eggs 38500-17048, 2007-38500-18593, and 2008-38500-19230 in a timely manner. Steve Boggio, Tracy J. Brown, Jana from the United States Department of Agriculture L. Cole, Rebecca Cooper, Elijah Cureton, Jason Frost, Cooperative State Research, Education, and Extension Kerry Grande, Ron Hardy, Chris Nelson, Lucas Porter, Service. Other financial support was provided by the Jay Pravacek, Elizabeth Scriven, Mariah Talbott, John Cutthroat Chapter of Trout Unlimited Memorial Research Seals, and Niccole Wandelear were also extremely help- Fellowship, the Gregory L. Bonham Memorial Scholarship, ful with their administrative, financial, and technical and Colorado State University. assistance on this project. References to trade names or We thank all members of the Western Regional manufacturers do not imply government endorsement of Aquaculture Center at the School of Aquatic and Fishery commercial products. These studies could not have been Sciences, University of Washington for their financial and completed without help from and use of the U.S. Fish and administrative support for this and all other Inland Wildlife Service’s Bozeman Fish Technology Center and Native Trout Culture Workgroup projects. We also thank University of Idaho’s Hagerman Fish Culture Experiment the Yellowstone River State Fish Hatchery and Jackson Station staff and facilities.

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